1. Field of the Invention
The present invention relates to a novel .beta.-amylase gene.
2. Description of the Prior Art
.beta.-amylase is an enzyme acting on starch to cut the .alpha.-1,4-glucoside bond from the non-reducing terminal into a maltose unit and form .beta.-maltose. Not many microorganisms are known to produce .beta.-amylase, and in industry there is used a .beta.-amylase derived from soybean which has an optimal temperature of about 60.degree. C.
Clostridium thermosulfurogenes is a thermophilic obligate anaerobe with high starch decomposition ability and extracellularly secretes thermophilic .beta.-amylase (Japanese Patent Disclosure No. 62-500422). This thermophilic .beta.-amylase has an optimum temperature of 75.degree. C. and is stable to heat even at 85.degree. C. Although the optimum pH thereof ranges from 5.5 to 6.0, the thermophilic .beta.-amylase is stable in the pH range of from 3.5 to 6.5. Further, this .beta.-amylase is an SH enzyme which is inactivated with SH reagents such as PCMB (parachloromercuribenzoate), iodo acetate, Cu.sup.2+ and Hg.sup.2+. Among these properties, the thermostability is particularly superior to that of the .beta.-amylase derived from soybean and other sources. It is expected that the thermophilic .beta.-amylase from Clostridium thermosulfurogenes will be a very useful enzyme for industrial production of maltose and other sugars from starch.